1. Field of the Invention
The present invention relates to a fan motor of an air conditioner, and particularly, to a speed control system of a fan motor of an air conditioner.
2. Description of the Background Art
In general, a single-phase induction motor is used as a fan motor of an air conditioner. To generate a rotating torque, the signal-phase induction motor supplies both a magnetizing current generating a rotating magnetic field and an induced current generated in a rotor to windings connected to an external power terminal.
The single-phase induction motor has limit in improving efficiency by a primary copper loss and a secondary copper loss of a rotor. To solve such limit, an HIM (Hybrid Induction Motor) shown in FIGS. 1 and 2 is being used recently as a fan motor of the air conditioner. Hereinafter, an induction motor having a permanent magnet rotor is defined as an HIM.
FIG. 1 is a schematic sectional view of the HIM in accordance with the conventional art.
FIG. 2 is a schematic top view taken along line B–B′ of the HIM of FIG. 1.
As shown in FIGS. 1 and 2, a stator 102 is installed inside a bracket 101 of the HIM in accordance with the conventional art, and an induction rotor 103 is installed inside the stator 102. A plurality of slots 105 are protrudingly formed inside the stator 102, and coils 106 are respectively wound on the slots 105.
Aluminum rotor bars 107 are vertically inserted in a plurality of air gaps 103A formed at an edge of the rotor 103 in a vertical direction, and the aluminum rotor bars 107 are connected to each other by an end ring 108.
A rotating shaft 109 for transferring a rotary force of the rotor 103 to the outside is installed at an air gap 103B formed at the center of the induction rotor 103. The rotating shaft 109 becomes rotatable by an oilless bearing 110 installed at the bracket 101.
A permanent magnet rotor 104 for rotating the rotor 103 at a strong magnetic flux while being rotated by a rotating magnetic field generated from the stator 102 is installed between the stator 102 and the induction rotor 103.
When an AC voltage is applied to the HIM in accordance with the conventional art, the permanent magnet rotor 104 is rotated by a current applied to the coil 106 of the stator 102, and the rotated permanent magnet rotor 104 generates a rotating magnetic field having a strong magnetic flux, thereby rotating the induction rotor 103. At this time, the low inertial permanent magnetic rotor 104 separated from a fan (not shown) is rotated by the rotating magnetic field of the stator 102, and a torque generating magnetic flux is supplied to the induction rotor 103 by the rotating magnetic field of the permanent magnet rotor 104, so that the induction rotor 103 is rotated. Namely, when the permanent magnet rotor 104 rotated by an oval-shaped rotating field generated from the stator of distributing windings is rotated, the permanent magnet rotor 104 generates a rotating magnetic field having a strong magnetic flux, thereby rotating the induction rotor 103. Therefore, the HIM is operated at high efficiency, making a low noise.
Speed characteristics of the HIM and a general induction motor in accordance with the conventional art will now be described with reference to FIG. 3.
FIG. 3 is a graph showing a speed characteristic of the HIM and the general induction motor according to the conventional art.
As shown, when a speed control system of controlling a rotating speed of a fan motor by controlling a voltage applied to the fan motor (HIM) is applied to the HIM, a speed control range is restricted according to the voltage (e.g., 790˜880 rpm (revolution per minute)). Namely, because of the permanent magnet rotor 104, the speed control range is restricted within 790˜880 rpm. For this reason, the speed control system in accordance with the conventional art cannot be applied to the air conditioner requiring a speed control range of 100 rpm or more.
Meanwhile, an induction motor used as a fan motor of an air conditioner in accordance with the conventional art is disclosed in U.S. Pat. No. 6,819,026 registered on Nov. 16th in 2004.